Bibliography

SFTI-1 is a 14 amino acid, cyclic peptide found in the seeds of
Helianthus annus (sunflower) that is a potent inhibitor of
trypsin [9,8].
Intriguingly, SFTI-1 belongs to a class of Cys-rich trypsin
inhibitors called the Bowman-Birk Inhibitors (BBI) that are widely
distributed within plants of the Fabaceae (leguminous) and Poaceae
(graminaceous) families
[78,77]. BBIs from
the Fabaceae generally have a molecular weight of 8000 while
monocot BBIs, from the Poaceae, can be divided into two classes --
one of size 8000 and the other of 16000. The smaller
monocot BBIs have a single active site, while the dicot BBIs and the
larger monocot family both have two reactive loops, in most cases, one
targeting trypsin and one targeting chymotrypsin
[79]. The duplication of active loops
in this class of protein has led to them being referred to as ``double
headed'' proteins -- capable of inhibiting trypsin and chymotrypsin
in a 1:1:1 stoichiometry simultaneously
[80]. SFTI-1 shares strong
sequence homology with the trypsin inhibitory loop of the BBI family,
suggesting that this peptide may be a minimised version of an
ancestral BBI protein.

SFTI-1 was first reported at a conference in Italy where it was
described as an unidentified, M 1.5 kDa trypsin inhibitor
[81]. Subsequently this inhibitor was named SFTI-1
and its crystal structure in complex with trypsin was described
[9]. As was the case with the cyclotides, early
attempts to sequence the peptide were frustrated by the lack of an
N-terminus. In this case the sequence and cyclic nature of SFTI-1 were
eventually determined using a combination of amino acid analysis and
sequencing directly from the electron density in the crystal structure
[9]. In recent years a great deal of research has
centred on the production of minimised polypeptides mimicking the
active site of proteins with biologically important activity and the
reactive loop of the BBI family has attracted attention as a minimal
peptide inhibitor of trypsin
[84,82,85,83].
SFTI-1, which appears to be a cyclic version of a BBI trypsin reactive
loop, is the most potent known inhibitor of trypsin
[8,9].

CyBase is managed at the Institute of Molecular Bioscience IMB, Brisbane, Australia.

The database and computational tools found on this website may be used for academic research only, provided that it is referred to CyBase, the database of cyclic proteins (http://www.cybase.org.au). For any other use please contact David Craik (d.craik@imb.uq.edu.au).